srcset shortcode function for wordpress - returns srcset from image attachment id

srcset-shortcode-wordpress.php

add_shortcode('srcset', 'srcset_func');

function srcset_func($attr)
{
	$images = array();
	foreach(get_intermediate_image_sizes() as $size){
		$images[] = wp_get_attachment_image_src($attr['attachment_id'], $size);
	}

	$srcset = ''; $count = 0;
	foreach($images as $image){ $count++;
		$srcset.= $image[0].' '.$image[1]. 'w' . ( $count == count($images) ? '' : ', ' );
	}

	return 'srcset="'. $srcset .'"';
}